In the case of performing work using an excavator or similar vehicle, the primary purpose of a float valve is to return hydraulic fluid to a hydraulic tank by making flow paths of the bore chamber side and rod chamber side of boom cylinders communicate with each other during a boom-down operation. In the prior art, the float function is usually achieved by a directional control valve with a special spool which has a “4th position” in which the pump supply is blocked and both cylinder ports are connected to the reservoir.